Based on gravity anomaly data and terrain elevation data(DEM(9″) and SRTM3(3″)),this paper calculates the gravity gradients and its power spectral density of two profiles in West Arnhem Land of Australia′s northern territory.We implement Remove-Recovery and Stokes integral method to obtain the outcomes.We also implement FFT methods to calculate the gravity gradients covering the entire area.The results show that combination of gravity anomaly data with high spatial resolution terrain elevation data can effectively improve the accuracy of gravity gradients.Calculated power spectral density matches well with the power spectral density model,it shows that power spectral density greater than 0.3 Hz can be regarded as noise.The results provide a reference for data processing in identifying and eliminating the noise in gradients.In addition,it provides beneficial exploration for reference map of gravity gradient assisted navigation and for gravity gradient measurement system calibration.
When modern-style plate tectonics started and operated on a specific old craton has been a hot topic involving the early Earth's evolution. In order to address this issue on the evolution of the Neoarchean North China Craton (NCC), we investigated a newly identified successive magmatic rock suite of tonalite-trondhjemite-granodiorite (TTG)-sanukitoid in the Datong-Huai’an Complex. Geochemically, TTG gneisses in the Datong-Huai’an Complex can be divided into high-pressure (HP) and low-pressure (LP) TTG rocks. The HP TTGs are characterized by steep rare earth element (REE) patterns, obvious negative Nb, Ta and Ti anomalies and positive δEu anomalies, high Sr/Y, Nb/Ta and (La/Yb)N ratios, and positive Hf (t) (+2.1 to +8.7) and δ18O values (Ave 5.5‰ to 6.0‰). Their protolith is interpreted as the consequence of partial melting of a subducted oceanic slab with garnet and minor rutile as residual phases. The LP TTGs feature flat REE patterns, slightly negative Nb, Ta and Ti anomalies and negative δEu anomalies, low Sr/Y, Nb/Ta and (La/Yb)N ratios, positive Hf (t) (+3.4 to +5.9) and high δ18O values (Ave 5.9‰ to 6.1‰). They may have been generated by partial melting of mafic lower crust with residual plagioclase and amphibolite in the source. The sanukitoid rocks show high MgO, Cr and Ni concentrations but relatively low (La/Yb)N values, positive ɛHf (t) values (+1.5 to +5.4), and higher δ18O values (Ave 1.9‰ to 8.7‰), suggesting that they were originated from partial melting of mantle peridotite previously modified by slab-derived or sediment-derived melts. Zircon U–Pb dating results reveal that the HP TTGs formed at ~2538 Ma and ~2479–2441 Ma, whereas the LP TTGs and sanukitoids formed at ~2518 Ma and ~2517–2485 Ma, respectively. Combining rock assemblages, geochemical features and geological data, we propose that this long-lived magmatism can be divided into three stages of ~2.55-2.52 Ga, ~2.52-2.48 Ga and ~2.48-2.44 Ga. The Datong-Huai’an Complex may have developed along an active continental margin and depicts modern-style plate tectonics with continuous steep subduction, slab rollback and back-arc extension in the late Neoarchean.
The traditional pulsar period estimation method using a single distorted profile averts multiple epoch folding processes, but still has space for accuracy to improve. To give consideration to both accuracy and computational load, we combine the fast butterfly epoch folding (FBEF) with the single distorted profile (SDP)-based pulsar period estimation, and propose the FBEF-based pulsar period estimation with a few distorted profiles (FBEF-FDP), which merely uses a few epoch folding processes to enhance accuracy sharply. Firstly, the fast butterfly epoch folding is used to produce a few distorted pulsar profiles with different periods. And then the single distorted profile-based pulsar period estimation explores each distorted prolife to provide a corresponding distortion degree. Finally, using these distortion degree values, the nonlinear search method for multiple minimums can get an optimal distortion degree estimation. Besides, we prove that distortion degree estimation errors of different accumulative distorted profiles from the same pulsar photon sequence are incompletely correlated. This is the theorical basis that the distortion degree estimation values from the same pulsar photon sequence can be fitted to obtain more highly accurate distortion degree estimation. The computational complexity demonstrates that the computational load increases with the number of groups. Thus, to ensure the real-time of the FBEF-FDP, the number of groups should not be too large. Simulation results demonstrate that the accuracy of the fast butterfly epoch folding-based pulsar period estimation using a few distorted profiles enhances at the cost of a small computational load.
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